What are the pros and cons of slip ring induction motors?

Advantages of slip ring induction motor

Good starting performance

• High starting torque: The slip-ring induction motor can obtain a high starting torque by connecting an external resistance in the rotor circuit at the time of starting. This makes it ideal for situations where heavy loads need to be driven or where large inertia needs to be overcome. For example, in equipment such as cranes and compressors, slip ring induction motors can provide enough torque at the start moment to ensure that the equipment starts smoothly.

• Adjustable starting current: By adjusting the resistance in the rotor circuit, the size of the starting current can be controlled. This is important to avoid excessive impact on the power system. For example, in some cases where the power grid capacity is limited, the use of slip ring induction motors can achieve a smooth start without exceeding the power capacity limit by gradually reducing the rotor resistance, reducing the impact on other equipment.

High operational reliability

• Simple and strong structure: the structure of the slip ring induction motor is relatively simple, mainly composed of stator, rotor, slip ring and brush and other components. Most of these components are manufactured using mature manufacturing processes with high reliability and durability. For example, the stator and rotor windings are usually wrapped in a strong insulating material that can withstand a certain amount of temperature and mechanical stress. Although the slip ring and brush are vulnerable parts, they can also ensure a long service life under normal maintenance.

• Adaptability to harsh environment: slip ring induction motor has strong adaptability to environmental conditions. It can operate in harsh working environments, such as high temperature, high humidity, dust and so on. For example, in some industrial production sites, the environmental conditions are poor, but the slip ring induction motor can still operate stably, providing reliable power support for production.

Disadvantages of slip ring induction motor

High maintenance costs

• Slip ring and brush wear: During the operation of the slip ring induction motor, there will be friction between the slip ring and the brush, resulting in the wear of the slip ring and the brush. This requires regular inspection and replacement of slip rings and brushes, increasing maintenance costs. For example, in some high-load operation occasions, the slip ring and brush wear faster, may need to be replaced every few months, which not only increases the cost of materials, but also requires labor and time to maintain.

• Additional maintenance equipment is required: In order to ensure the normal operation of the slip ring induction motor, it is usually necessary to be equipped with some additional maintenance equipment, such as brush pressure adjustment device, slip ring cleaning device, etc. The acquisition and maintenance of such equipment also adds to the cost. For example, the brush pressure adjustment device needs to be calibrated and adjusted regularly to ensure good contact between the brush and the slip ring to avoid motor failure due to poor contact.

Relatively low efficiency

• Rotor resistance loss: Because the slip ring induction motor needs to adjust the performance through the resistance in the rotor circuit during start-up and operation, this will lead to a certain power loss. Especially during operation, the loss on the rotor resistance will reduce the efficiency of the motor. For example, compared with other types of motors, the input power of a slip ring induction motor may be higher for the same output power, resulting in a waste of energy.

• The contact resistance between the slip ring and the brush: The contact resistance between the slip ring and the brush will also produce a certain power loss. Although the contact resistance is usually small, it will still have a certain impact on the efficiency of the motor in the case of high current operation. For example, in some high-power slip-ring induction motors, the loss on the contact resistance can reach several kilowatts, which is a disadvantage for the efficient use of energy.